The subject matter disclosed herein relates generally to drive mechanisms for variable diameter rotor systems, and in particular to individual driven mechanisms for retraction/extension of rotor blades.
A tilt rotor or tilt wing aircraft typically employs a pair of rotor systems which are pivotable such that the rotors may assume a vertical or horizontal orientation. In a horizontal orientation (i.e., horizontal rotor plane), the aircraft is capable of hovering flight, while in a vertical orientation (i.e., vertical rotor plane), the aircraft is propelled in the same manner as conventional propeller-driven fixed-wing aircraft.
Variable Diameter Rotor (VDR) systems are known to provide distinct advantages. That is, when the plane of the rotor is oriented horizontally, the rotor diameter is enlarged for improved hovering efficiency and, when oriented vertically, the rotor diameter is reduced for improved propulsive efficiency.
Existing VDR drive mechanisms are described in U.S. Pat. No. 5,642,982, U.S. Pat. No. 5,636,969, U.S. Pat. No. 6,578,793, U.S. Pat. No. 4,142,697, U.S. Pat. No. 6,454,532 and U.S. Pat. No. 6,655,915, U.S. Pat. No. 6,030,177 and U.S. Pat. No. 6,019,578. The entire contents of these patents are incorporated herein by reference. While these VDR drive mechanisms are well suited for their intended purposes, and some employ the use of a multi-fiber strap, a need exists to reduce the amount of torsional fatigue in the strap. Also, there needs to be a method of monitoring strap elongation, so that a strap can be replaced on condition.